Four people have been arrested and a Homeland Security officer is under investigation for firing his weapon during a weekend scuffle between pro-Israel demonstrators and Palestinian supporters outside the Federal Building in Los Angeles.

The altercation Sunday evening grew out of a shouting match between the occupants of two vehicles that escalated when several people from one vehicle were assaulted by suspects in the other, the Los Angeles County Sheriff’s Office said.

An officer of the Federal Protective Service, an agency of the U.S. Department of Homeland Security, who witnessed the assault intervened and fired his weapon, but no one was hit by gunfire or otherwise injured, Sheriff’s Sergeant Carmen Arballo said.

She said four suspects were arrested. According to the City News Service, the four were booked on suspicion of assault with a deadly weapon after some of those involved in the melee were seen brandishing wooden poles.

It was not clear whether the officer’s gun was fired deliberately or by accident. The sheriff’s office said the shooting was under investigation.

According to KNBC, the clash erupted when Palestinian supporters drove up in a truck and thrust a Palestinian flag out of the window.

Pro-Israel demonstrators grabbed the flag, threw to the ground and stomped on it, leading to a brawl when the Palestinian supporters got out of their truck and one was stomped and kicked as he bent down to retrieve the flag, KNBC reported.

The confrontation occurred at the end of a rally by an estimated 500 demonstrators in support of Israel’s bombardment of the Gaza Strip in retaliation for rockets fired into Israel by Palestinian militants. A similar protest had been held at the same location on Saturday by Palestinian supporters condemning Israeli bombing of Gaza.